About the interview: Write a two-way data binding for Vue

<p id="app">
    <form>
      <input type="text"  v-model="number">
      <button type="button" v-click="increment">增加</button>
    </form>
    <h3 v-bind="number"></h3>
  </p>

 1. 一个input，使用v-model指令
 2. 一个button，使用v-click指令
 3. 一个h3，使用v-bind指令。

var app = new myVue({
      el:'#app',
      data: {
        number: 0
      },
      methods: {
        increment: function() {
          this.number ++;
        },
      }
    })

function myVue(options) {
  
}

function myVue(options) {
  this._init(options);
}
myVue.prototype._init = function (options) {
    this.$options = options;  // options 为上面使用时传入的结构体，包括el,data,methods
    this.$el = document.querySelector(options.el); // el是 #app, this.$el是id为app的Element元素
    this.$data = options.data; // this.$data = {number: 0}
    this.$methods = options.methods;  // this.$methods = {increment: function(){}}
  }

 myVue.prototype._obverse = function (obj) { // obj = {number: 0}
    var value;
    for (key in obj) {  //遍历obj对象
      if (obj.hasOwnProperty(key)) {
        value = obj[key]; 
        if (typeof value === 'object') {  //如果值还是对象，则遍历处理
          this._obverse(value);
        }
        Object.defineProperty(this.$data, key, {  //关键
          enumerable: true,
          configurable: true,
          get: function () {
            console.log(`获取${value}`);
            return value;
          },
          set: function (newVal) {
            console.log(`更新${newVal}`);
            if (value !== newVal) {
              value = newVal;
            }
          }
        })
      }
    }
  }
 
 myVue.prototype._init = function (options) {
    this.$options = options;
    this.$el = document.querySelector(options.el);
    this.$data = options.data;
    this.$methods = options.methods;
   
    this._obverse(this.$data);
  }

function Watcher(name, el, vm, exp, attr) {
    this.name = name;         //指令名称，例如文本节点，该值设为"text"
    this.el = el;             //指令对应的DOM元素
    this.vm = vm;             //指令所属myVue实例
    this.exp = exp;           //指令对应的值，本例如"number"
    this.attr = attr;         //绑定的属性值，本例为"innerHTML"

    this.update();
  }

  Watcher.prototype.update = function () {
    this.el[this.attr] = this.vm.$data[this.exp]; //比如 H3.innerHTML = this.data.number; 当number改变时，
    会触发这个update函数，保证对应的DOM内容进行了更新。
  }

myVue.prototype._init = function (options) {
    //...
    this._binding = {};   //_binding保存着model与view的映射关系，也就是我们前面定义的Watcher的实例。
    当model改变时，我们会触发其中的指令类更新，保证view也能实时更新
    //...
  }
 
  myVue.prototype._obverse = function (obj) {
    //...
      if (obj.hasOwnProperty(key)) {
        this._binding[key] = {    // 按照前面的数据，_binding = {number: _directives: []}                                                                                                                                                  
          _directives: []
        };
        //...
        var binding = this._binding[key];
        Object.defineProperty(this.$data, key, {
          //...
          set: function (newVal) {
            console.log(`更新${newVal}`);
            if (value !== newVal) {
              value = newVal;
              binding._directives.forEach(function (item) {  // 当number改变时，
              触发_binding[number]._directives 中的绑定的Watcher类的更新
                item.update();
              })
            }
          }
        })
      }
    }
  }

 myVue.prototype._init = function (options) {
   //...
    this._complie(this.$el);
  }
 
myVue.prototype._complie = function (root) { root 为 id为app的Element元素，也就是我们的根元素
    var _this = this;
    var nodes = root.children;
    for (var i = 0; i < nodes.length; i++) {
      var node = nodes[i];
      if (node.children.length) {  // 对所有元素进行遍历，并进行处理
        this._complie(node);
      }

      if (node.hasAttribute(&#39;v-click&#39;)) {  // 如果有v-click属性，我们监听它的onclick事件，触发increment事件，
      即number++
        node.onclick = (function () {
          var attrVal = nodes[i].getAttribute(&#39;v-click&#39;);
          return _this.$methods[attrVal].bind(_this.$data);  
          //bind是使data的作用域与method函数的作用域保持一致
        })();
      }

      if (node.hasAttribute(&#39;v-model&#39;) && (node.tagName = &#39;INPUT&#39; || node.tagName == &#39;TEXTAREA&#39;)) { 
      // 如果有v-model属性，并且元素是INPUT或者TEXTAREA，我们监听它的input事件
        node.addEventListener(&#39;input&#39;, (function(key) {  
          var attrVal = node.getAttribute(&#39;v-model&#39;);
           //_this._binding[&#39;number&#39;]._directives = [一个Watcher实例]
           // 其中Watcher.prototype.update = function () {
           //    node[&#39;vaule&#39;] = _this.$data[&#39;number&#39;];  这就将node的值保持与number一致
           // }
          _this._binding[attrVal]._directives.push(new Watcher(  
            &#39;input&#39;,
            node,
            _this,
            attrVal,
            &#39;value&#39;
          ))

          return function() {
            _this.$data[attrVal] =  nodes[key].value; // 使number 的值与 node的value保持一致，
            已经实现了双向绑定
          }
        })(i));
      } 

      if (node.hasAttribute(&#39;v-bind&#39;)) { // 如果有v-bind属性，我们只要使node的值及时更新为data中number的值即可
        var attrVal = node.getAttribute(&#39;v-bind&#39;);
        _this._binding[attrVal]._directives.push(new Watcher(
          &#39;text&#39;,
          node,
          _this,
          attrVal,
          &#39;innerHTML&#39;
        ))
      }
    }
  }

  



  <p id="app">
    <form>
      <input type="text"  v-model="number">
      <button type="button" v-click="increment">增加</button>
    </form>
    <h3 v-bind="number"></h3>
  </p>


<script>
  function myVue(options) {
    this._init(options);
  }

  myVue.prototype._init = function (options) {
    this.$options = options;
    this.$el = document.querySelector(options.el);
    this.$data = options.data;
    this.$methods = options.methods;

    this._binding = {};
    this._obverse(this.$data);
    this._complie(this.$el);
  }
 
  myVue.prototype._obverse = function (obj) {
    var value;
    for (key in obj) {
      if (obj.hasOwnProperty(key)) {
        this._binding[key] = {                                                                                                                                                          
          _directives: []
        };
        value = obj[key];
        if (typeof value === &#39;object&#39;) {
          this._obverse(value);
        }
        var binding = this._binding[key];
        Object.defineProperty(this.$data, key, {
          enumerable: true,
          configurable: true,
          get: function () {
            console.log(`获取${value}`);
            return value;
          },
          set: function (newVal) {
            console.log(`更新${newVal}`);
            if (value !== newVal) {
              value = newVal;
              binding._directives.forEach(function (item) {
                item.update();
              })
            }
          }
        })
      }
    }
  }

  myVue.prototype._complie = function (root) {
    var _this = this;
    var nodes = root.children;
    for (var i = 0; i < nodes.length; i++) {
      var node = nodes[i];
      if (node.children.length) {
        this._complie(node);
      }

      if (node.hasAttribute(&#39;v-click&#39;)) {
        node.onclick = (function () {
          var attrVal = nodes[i].getAttribute(&#39;v-click&#39;);
          return _this.$methods[attrVal].bind(_this.$data);
        })();
      }

      if (node.hasAttribute(&#39;v-model&#39;) && (node.tagName = 
      &#39;INPUT&#39; || node.tagName == &#39;TEXTAREA&#39;)) {
        node.addEventListener(&#39;input&#39;, (function(key) {
          var attrVal = node.getAttribute(&#39;v-model&#39;);
          _this._binding[attrVal]._directives.push(new Watcher(
            &#39;input&#39;,
            node,
            _this,
            attrVal,
            &#39;value&#39;
          ))

          return function() {
            _this.$data[attrVal] =  nodes[key].value;
          }
        })(i));
      } 

      if (node.hasAttribute(&#39;v-bind&#39;)) {
        var attrVal = node.getAttribute(&#39;v-bind&#39;);
        _this._binding[attrVal]._directives.push(new Watcher(
          &#39;text&#39;,
          node,
          _this,
          attrVal,
          &#39;innerHTML&#39;
        ))
      }
    }
  }

  function Watcher(name, el, vm, exp, attr) {
    this.name = name;         //指令名称，例如文本节点，该值设为"text"
    this.el = el;             //指令对应的DOM元素
    this.vm = vm;             //指令所属myVue实例
    this.exp = exp;           //指令对应的值，本例如"number"
    this.attr = attr;         //绑定的属性值，本例为"innerHTML"

    this.update();
  }

  Watcher.prototype.update = function () {
    this.el[this.attr] = this.vm.$data[this.exp];
  }

  window.onload = function() {
    var app = new myVue({
      el:&amp;#39;#app&amp;#39;,
      data: {
        number: 0
      },
      methods: {
        increment: function() {
          this.number ++;
        },
      }
    })
  }
</script>